1. Field of the Disclosure
The present disclosure relates to a projection system, and more particularly, to a projection system having a high optical efficiency and a fast optical modulation speed.
2. Description of the Related Art
Recently, while display devices are becoming lighter and thinner, the size of screens of the display devices are increasing. A projector or projection TV is a typical display capable of providing a large screen. Micro-display devices that are the results of new technology for projection systems include transmission type LCD (liquid crystal display) panels, reflection type LCOS (liquid crystal on Silicon) panels, and DMD (digital micro mirror device) panels. Also, micro-display devices include a one-panel method, a two-panel method, and a three-panel method according to how many micro-display devices are used. The three-panel method is common to transmission type LCD panel displays while the one-panel method is generally used by DMD panel displays. For LCOS panels, all of the one-panel method, two-panel method, and three-panel method are used.
FIG. 1 is a perspective view showing the configuration of a conventional projection system using a transmission type LCD. Referring to FIG. 1, a projection system using a transmission type LCD includes a light source 10, two dichroic mirrors 15a and 15b that split light emitted from the light source 10 into red, green, and blue lights, LCD panels 20a, 20b, and 20c modulating the lights split by the dichroic mirrors 15a and 15b and changing a path thereof by three mirrors 18, according to an input signal, and a color combining prism 25 combining images of the LCD panels 20a, 20b, and 20c. 
However, this projection system employing the three-panel method has a bulky structure and the optical efficiency of the projection system is low because a polarizer that is an essential part of each of the LCD panels 20a, 20b, and 20c has a high light absorption characteristic. Also, in the LCD panel method, since light is modulated by the alignment of liquid crystal between alignment films, returning of the liquid crystal according to a control signal to its original alignment direction takes some time so that a modulation speed is slow.
FIG. 2 is a perspective view showing the configuration of a conventional one-panel type DLP (digital light processing) projection system using a DMD panel. Referring to FIG. 2, a DLP projection system includes a light source 30, a color filter 35 sequentially splitting red, green, and blue lights according to time, a DMD 40 sequentially displaying screen information of each color, and a projection lens 45 projecting the light from the DMD 40 onto a screen.
The projection system employing the DMD can adopt the one-panel method because the optical efficiency is higher than a case using the LCD panel. Thus, the number of optical parts can be reduced. However, the DMD is supplied only by Texas Instruments Incorporated in the U.S. Furthermore, the DLP projection system has a halo effect that a gray band occurs around an image by stray light that is bounced off the edges of the micro-mirrors of the DMD.